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Mikes 1.5JZ 6875 – 1000BHP Torquemonster

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Full spec list can be found here: Clicky

Summary of the important parts

Engine Type 
1.5JZ VVTi 
Single Turbo
10:1 Compression Ratio (Estimated 9:5:1 Dynamic Compression)

Engine Spec 
Stock Head, Ports & Valves (1JZGTE VVTI)
BC 272 Camshafts with Titanium Springs & Retainers
2JZGE Block with Manley Turbo Tuff Rods & Manley 87mm Platinum Pistons
Stock Crank & Stock Main Caps
ARP Hardware for rods, mains, head, flywheel 
Turbo & Intake
Precision 6875 Gen 2 DBB 0.96 A/R Open Housing
Stock 1JZ Inlet with 76 Hitachi DBW throttle

Fuel System
ASNU 1500 Injectors
PHR Triple Pump Hanger with 3 x 485 Pumps

4’’ SRD Downpipe & 4’’ Dual Box Whifbitz Catback S/S
Modified Walton 1JZ T4 Open Scroll Manifold 
Turbosmart 60mm GenV Progate Wastegate with 1.3 Bar Spring (Recirc)
Late Style R154 with PGS Dog engagement HD Gearset
Xtreme 230mm Rigid Twin Disc 
A03B Diff (3.26) with OS Giken Superlock

Syvecs S7+ 
All the sensors. 

Dyno & Mapped 
Mike SRD

Maximum Power Figures on Shell Vpower
1.7 Bar 
671 RWHP (~750BHP) & 666 ft.lbs torque
Estimated 12% Driveline Loss with SAE Correction

Maximum Power Figures on VP C85 Ethanol
2.3 Bar
905RWHP (~1010BHP) & 875 ft.lbs torque
Estimated 12% Driveline Loss with SAE Correction

Wastegate - Shell VPower



1.7 Bar - Shell VPower


2.3 Bar - VP C85 Ethanol 




Will have a follow up post with a write up on some of the goals, testing done and some neat data on this setup for anyone interested in my ramblings. Big thanks to Lee P who helped get me over the finish line with the build. 


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Incredible work mate. Decent amount of work in that bay.

How come you chose 6875?

Seen a few people also using a stock head. Any reason you didn't open it up or go larger valves. Read a few people think valves aren't needed. Curious to know your thoughts.

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Thanks guys. 

Here's some more info on the reasons for the build and some of the data gathered. 

For the last few years I’ve been tinkering with using 1JZ heads on 2J bottom ends. Initially this was due to a cost saving whilst having a rudimentary 1JZ single turbo setup with a blown bottom end. This current iteration is my 3rd engine. Initially I started with a budget spec build (380rwhp), then OEM+ (500rwhp) and now onto fully forged setup.

There has always been a debate on the pros & cons of using a 1JZ head, and I set out many moons ago to try and gather some data that I could relay back to community from experience rather than hearsay.

From my own experience I had seen that previously 1.5JZ’s always struggled to hold power at high rpm, even with cams, aftermarket inlets etc but never had the chance to see one that was a hardcore build and compare that to another hardcore 2J build, whilst on the same dyno. But now I can!

So, for the third iteration of the build I set out to shed some light on the following:

1) Build a high compression 1.5JZ using a stock port head and stock valves.
Equip the engine with an unrestrictive intake/exhaust setup, and then use alcohol to push the setup to a safe maximum limit and see if the point at which the head becomes restrictive can be identified.

2) Identify expected behavior of what you could expect to see between using a 1.5JZ versus a 2JZ.

3) Typically we see 6870 turbo struggle to hold target boost (2Bar+) after 7.5k rpm. Using an exhaust gas pressure sensor mounted on the exhaust manifold, could a noticeable difference between a 6870 and a 6875 precision turbo be identified. Is this problem related to compressor efficiency or exhaust pressure or both?


1.5JZ VVTi Performance versus 2JZ VVTi 

Example A

Both engines using stock inlets, both with cams. Same gear ratio's used. 

This is at 1.8 Bar of boost on pump fuel.

Both graphs are fairly similar. Spool is essentially the same, however you can see the 1JZ continues building torque where the 2JZ starts leveling off.

However, after 6'000rpm you can see the 1JZ is starting drop torque fairly quickly compared to 2JZ, and the power is on the decline as well. 

The 2JZ on the other hand looks like it wants to keep making power if it was allowed to rev higher. This was a stock bottom end 2J so limiter was sensible around 7000. 



Example B

My 1.5JZ versus Luc's 2JZ VVTI with headwork & aftermarket inlet.

Both engines are running 2.3 Bar on Ethanol fuel. Both using the same gear ratio. 

At this sort of boost level we can really start to see the differences in an unrestricted 1.5JZ versus 2JZ. 

Spool is again fairly similar, but the 1.5JZ makes ~200 ft.lbs more torque when target boost is achieved and similar again for peak torque on both engines. 

What we could start seeing on the last graph is really obvious now.

The 1.5JZ is done making power at 7k, wheras the 2J is just starting to warm up and starts pulling for another 1500rpm. 

I found it interesting that both engines make the same power at the same boost, as they should have similar airflow being provided by the turbo. But the way that each engine processes that airflow is quite cool. 


1JZ VVTI Head Conclusion

I'm quite pleased with the results from this experiment. I think the stock head does well for what it is, but its obvious that the smaller head chamber volume & smaller exhaust ports are geared towards providing airflow velocity and torque lower down for its designed 1JZ displacement.

Once strapped to a 2J, its clear to see that the engine can get the air into the engine quickly and effieciently, but struggles to get the air out once the RPM increases, choking itself and causing a bottleneck.

I might revisit the head at some point and go extreme with porting and valves and see what that does to the setup. But I have a feeling that the 1JZ head still won't flow as well as a 2J that has similar porting. The design of both heads will be hard to change even with a lot of porting. 

Have yet to see a 2JZ using a 3.0 bottom end come close to matching the torque output of this setup.  The only 2J that has matched its torque with similar boost is a 3.4 stroker 6870 build. 

So I guess the take away from this is that if you want a responsive high torque midrange setup, then a 1.5JZ is a nice way to go. Probably why its so popular with drifters, its essentially a stroker than can be put together fairly frugally without having to go to a 3.4 build. Just be sure to have a budget to beefen your driveline, high torque output will takes it's toll. 

For performance under 7000rpm 1.5JZ can match and sometimes exceed 2JZ performance, depending on what parts are used on build. 

If you want to make your power at 7500 rpm or more then 2J is still going to be leading the way.


Precision 6870 GEN II versus 6875 GEN II

A problem we have seen at SRD with 6870 GEN II turbo is that after ~7500rpm, the wastegate solenoid duty has to be increased in order to maintain a target boost of 2 Bar or higher. After 8000rpm the wastegate duty basically maxes out and we start dropping boost, eventually back to around 1.8 Bar. If you run more than 2.2Bar of boost then the problem becomes even more noticable at high rpm as the boost drops off even more aggressively. 

To some degree this is expected as 6870 is only a midframe turbo with what is a fairly small compressor. Modern turbo tech allows such a small wheel to push out 900whp without much fuss and even 1000whp if you really wind it out. But there is a limit to all good things. 

So I decided to grab a 6875 GENII turbo for my build and stick an exhaust pressure sensor on the manifold as well as a pre intercooler temperature sensor in order to have some vague idea on what the compressor and turbine effiency might be doing. The idea was that maybe the extra 5mm on the turbine side would help alleviate any potential exhaust backpressure issues experienced on the 6870's smaller turbine. 

One thing I didn't envision whilst planning this was that the 1.5JZ wouldn't want to make much power after 7k, so my results aren't going to be a good comparison to a normal 2J build that revs to 8k or more. However there is still some interesting data. 

The below is a snapshot from a log done at 2.3 Bar of boost. 

Between 3500-6500rpm the exhaust pressure is less than my intake manifold pressure. This is great, it means the turbo is not fighting a restriction to make power and is an indication that efficient power is being produced by the rest of the intake/exaust system. 

After 7000rpm you can see the exhaust pressure goes higher than intake manifold pressure. Now we start moving into the realms of the turbo having to work harder for its power. As my rev limiter kicking in around 7500 the MAP/EMAP ratio at this point is ~1.05. Which to be fair is still pretty good, the turbo isn't working too hard yet. Unfortunately there is where the restriction on my head starts kicking in and I can't produce anymore power, so I don't rev it any further. 

However one could make the reasonable assumption that with another 1000rpm, the exhaust pressure will continue to rise. Until eventually the turbo has too much backpressure to work against and we start dropping boost. One would also assume that if Precision designed their turbo's well, that the efficiency of the turbo compressor would also start to tail off at around the same point where they expect their exhaust pressure to start rising beyond a wanted level. Was hoping to awnser that question for certain but will have to drop these sensors onto another setup and try again in the future. 

Overall from what I've seen on my setup and a few others. I don't think the extra $100 on a 6875 is worth it, not on a high revving 2JZ at least. Results are very similar to 6870, which is still king when it comes to power output vs response for a street turbo. If high RPM horsepower is your goal, better off going to a 7275 or larger. 



Hope you enjoyed that massive wall of text. 

Shall try to get some video's up as well soon. 

Edited by Mike2JZ (see edit history)
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Amazing post !!!

WOOW you are one of the very few guys who give a Supra quality to this forum, i wish I knew half of your knowledge !

Lee must keep you whatever you cost to him :p

I'm speachless in front of your post and will read/study it this evening !

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That's class. Congrats on breaking the 1000hp mark as well Mike, I'll bet that's a blast to drive in

Part 2 of the investigation...try to attain the best of both worlds? Low down performance of the 1.5J combined with the red line pulling power of a 2J 😎

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